Title of Invention

AN IMPROVED PROCESS FOR PREPARATION OF ULTRA-LIGHT HYDRATED ALUMINA

Abstract

The present invention describes an improved process for preparation of ultra-light hydrated alumina from aluminium salts/ Bayer"s liquor. The main features of this invention are, (a) to obtain hydrated alumina having tap density in the range of 0.098 to 0.32 g/cc, (b) to achieve the precipitation efficiency of less than 99%, (c) to instantaneously precipitate hydrated alumina by hydrothermally treating the Al3+ solution containing urea (Urea/ Al3+ mole ratio between 2:1 to 4:1) in the temperature range of 160 to 180 deg.C. The precipitate thus obtained is filtered, washed and dried to obtain the desired product.

Full Text

The invention relates to an improved process for preparation of ultra-light hydrated alumina. Particularly this invention relates to the hydrothermal preparation of light hydrated alumina having tap density in the range of 0.098 g/cc to 0.32 g/cc using different sources of aluminum. Special grade alumina and alumina precursors constitute about 10% of the total alumina production in the world. Due to their wide industrial applications, their production is increasing year after year. The major consumption of non-metallurgical grade alumina precursors is in industries specially catering to the need of polymer filter, paper, paint and pigments, ink, pharmaceutical and high tech ceramics/ refractories. Due to their non-toxic and easy to handle character, new areas of applications are being explored regularly. The suitability of a product for a particular use depends upon its particle size, surface area, thermal behavior, morphology and tap density. Low tap density alumina precursors are particularly useful in printing ink and wax polish industries. India has a large market for these products (more than Rs 300 crores), but does not produce them indigenously and the entire demand is met through imports. The earlier commercial/ laboratory processes so far available for preparing special grade hydrated alumina may be classified into: (i) Controlled precipitation from Bayer's liquor by using special grade seeds, surfactants, modifiers etc. (Y. Shibue, A. Sakamoto, Y.Kawai and M. Morihira. Light Metals, 1989, p 27-32; B. K. G.Baska, G. Szalay, F. Vallo, Light Metals, 1992, p17-24; B.K.Satapathy, P.Das, Light Metals, 1994,-147-153. (2) Mechanical and chemical treatment of metallurgical grade alumina precursors/alumina trihydrate (W.C. Sleppy, A.Pearson, C.Misra and G. MaeZura, Light Metals, 1991, p 118). (3) By sol-gel technique, utilizing various organic and inorganic salts of aluminum and Na2C03, NaHC03, urea etc. (S.Huijuan, M.Minghua, L.Huanzhen; K.Ying; T.Changyuan, Youse jinshu, 1990, 42(4), p 53-57; S. Taichi, S.Keiichi and O. Hiroaki, Chem. Express, 1990, 5(6), p 361-364 (Japan); J.L.Shi, J.H. Gao and Z.X.Lin, Report 1994, ISTIC-TR-94342, order No. PB-248019, p 1-9 (Eng); I. Masamichi, T. Yashiaki, T.Yasushi, Y.K.Kimura and M.I. Takahiro, Patent No. Ger.Offen.DE 19,522,946 (CI C01F7/00), 4 Jan 1996, JP Appl 94/143,678 24Jun.l994 10 pp (Ger); O, Mitsushige, I.Hiroshi, Patent No.[93,270,819], C1.C01F7/02) Japan 5pp, 1996). The main disadvantages of the processes (i) and (iii) are, (a) the precipitation time is very long ( from 6 to 48 hours), (b) the precipitation efficiency is about 60-80%, needing recycle of the filtrate, (c) use of seeding agents and (c) close control of precipitation conditions. The disadvantage of process (ii) is that it constitutes a number of process steps. Therefore, to overcome these shortcomings an improved process has been developed with less number of process steps, more precipitation efficiency, easily controllable precipitation conditions and shorter precipitation time. None of the available literature reports hydrated alumina with such low tap density as is being reported in the present invention The main object of the present invention is to prepare ultra-fine hydrated alumina hydrothermally from Al-salt solutions using urea as the precipitating agent. Another object of the of the present invention is to prepare light hydrated alumina with impurities within the acceptable limits from Bayer's liquor. Yet another object of the present invention is to reduce the precipitation time for obtaining ultra-light hydrated alumina. Accordingly the present invention provides an improved process for the preparation of ultra-light hydrated alumina from Bayer's liquor or Al salt solution which comprises a) preparing Al3+ solution in a concentration ranging from 1,5 to 6.0 g/1, b) adjusting the pH of the above said solution if needed to about 3 by adding H2S04, c) adding urea to the above said pH adjusted Al 3+solution in a molar ratio of urea to Al3+ solution in the range of 2:1 to 4:1 followed by hydrothermal precipitation in an autoclave at a temperature ranging from 160-180 °C to obtain the desired ultra-light hydrated alumina. In an embodiment of the present invention the ultra-light hydrated alumina obtained has a tap density in the range of 0.098 to 0.32 g/cc In yet another embodiment the precipitation efficiency ultra-light hydrated alumina is >99% . Novelty of the present invention is (a) preparation of ultra-light hydrated alumina having tap density varying between 0.089 to 0.32 g/cc using aluminum salt solution or Bayer's liquor (b) using urea as a precipitant at high temperature and (c) to carry out instantaneous precipitation of hydrated alumina at 160 to 180°C. The following examples are given to illustrate how the process of the present invention is carried out in actual practice and should not be construed to limit the scope of the invention. Example 1 Bayer's liquor {NaAl(OH)4} obtained from National Aluminum Company (NALCO) India, containing 80 g/1 aluminum, was first diluted with water to obtain 1.5 g/1 Al3+. Sulphuric acid was added to adjust the pH from 13.5 to 2.9 with vigorous agitation. To this solution calculated amount of urea to get urea/Al3+ ratio of 2 was added and the contents were transferred to an autoclave of 7.5 liter capacity for hydrothermal precipitation at a temperature of 180°C. On achieving the desired temperature the autoclave was switched off and allowed to cool. The products were washed with distilled water till the filtrate was free of sulphate (tested with BaCl2 solution) and then dried at ~100°C for 12 hours. The filtrate did not contain any aluminum ensuring its complete precipitation. At 180°C urea hydrolyses rapidly, resulting in instantaneous precipitation of hydrated alumina. The particle size of the precipitated product was in the range of 0.5 to 2.5 um and the impurity content [in terms of % by wt. of Na20+Fe203+Si02] was 0.4. The tap density of the product was 0.32 g/cc and weight loss on ignition (the precipitate was heated at 1000°C for one hour) was 26 67% Example-2 Bayer's liquor {NaAl(OH)4} obtained from National Aluminum Company (NALCO) India, containing 80 g/1 aluminum, was first diluted with water to obtain 6.0 g/1 Al3+. Sulphuric acid was added to adjust the pH from 13.5 to 2.9 with vigorous agitation. To this solution calculated amount of urea was added to obtain urea/Al3+ ratio of 4 and the contents were transferred to an autoclave of 7.5 liter capacity for hydrothermal precipitation at a temperature of 180°C. On achieving the desired temperature the autoclave was switched off and allowed to cool. The precipitate was washed with distilled water till the filtrate was free of sulphate (tested with BaCl2 solution) and then dried at 90°C for 12 hours. Quantitative precipitation of Al was obtained as there was no residual aluminum present in the filtrate. The tap density of the product was 0.098 g/cc and weight loss on ignition (the precipitate was heated at 1000°C for one hour) was 18.52%. Example-3 Chemical grade A12(S04)3.18H20 was dissolved in distilled water. The concentration of Al3+ was adjusted to 3.6g/l. A calculated amount of urea was added to this solution to obtain urea/Al mole ratio as 2. The contents were transferred to an autoclave and heated at 180°C. The rest of the procedure was same as given in earlier examples 1 and 2. The precipitation efficiency was ~99.5%. The tap density of the product was 0.182g/cc and weight loss on ignition was 22.11%. Example-4 Chemical grade A1(N03)3.9H20 was dissolved in distilled water. The concentration of Al3+ was adjusted to 5.4g/l. A calculated amount -concentration of Al3+ contents were transferred to an autoclave and heated at 160°C. The rest of the procedure was similar to the ones given in earlier examples 1 and 2. The precipitation efficiency was ~99.4%. The tap density of the product was 0.166g/cc. The main advantages of the process are : 1. The process is simpler in comparison to earlier processes. Here the process steps for preparation of light hydrated alumina are: adjustment of Al concentration and pH of the solution, addition of urea and heating the solution at 160-180°C inside an autoclave followed by filtration and drying of the product. 2. This process is superior to earlier processes in terms of precipitation efficiency and time of precipitation. 3. Due to rapid hydrolysis of urea in the temperature range of 160-180°C, precipitation completes spontaneously, thus this process can be made more efficient and economical by using a tube digester. 4. Since acidic Al3+ solutions are used for precipitation, bauxite digested in H2SO4 and purified for Fe and other trace metals can be used for commercial production of light hydrated alumina. 5. The chemicals used in this process are cheap and commercially available. 6. Bayer's liquor {NaAl(OH)4} can be used for production of ultra-light hydrated alumina.

Documents:

00073-del-2002 abstract.pdf

00073-del-2002 claim.pdf

00073-del-2002 coresspondence others.pdf

00073-del-2002 coresspoondence po.pdf

00073-del-2002 description complete.pdf

00073-del-2002 form-1.pdf

00073-del-2002 form-18.pdf

00073-del-2002 form-2.pdf

00073-del-2002 form-3.pdf

73-DEL-2002-Abstract-(26-10-2007).pdf

73-DEL-2002-Claims-(26-10-2007).pdf

73-DEL-2002-Correspondence-Others-(26-10-2007).pdf

73-DEL-2002-Description (Complete)-(26-10-2007).pdf

73-DEL-2002-Form-3-(26-10-2007).pdf